Oncolytic herpes simplex virus vectors and chemotherapy: are combinatorial strategies more effective for cancer?

Optimal strategies of oncolytic virus-bortezomib therapy via the apoptotic, necroptotic, and oncolysis signaling network

Bortezomib and oncolytic virotherapy are two emerging targeted cancer therapies. Bortezomib, a proteasome inhibitor, disrupts protein degradation in cells, leading to the accumulation of unfolded proteins that induce apoptosis. On the other hand, virotherapy uses genetically modified oncolytic viruses (OVs) to infect cancer cells, trigger cell lysis, and activate anti-tumor response. Despite progress in cancer treatment, identifying administration protocols for therapeutic agents remains a significant concern, aiming to strike a balance between efficacy, minimizing toxicity, and administrative costs. In this work, optimal control theory was employed to design a cost-effective and efficient co-administration protocols for bortezomib and OVs that could significantly diminish the population of cancer cells via the cell death program with the NF$ \kappa $B-BAX-RIP1 signaling network. Both linear and quadratic control strategies were explored to obtain practical treatment approaches by adapting necroptosis protocols to efficient cell death programs. Our findings demonstrated that a combination therapy commencing with the administration of OVs followed by bortezomib infusions yields an effective tumor-killing outcome. These results could provide valuable guidance for the development of clinical administration protocols in cancer treatment.

Combination of novel oncolytic herpesvirus with paclitaxel as an efficient strategy for breast cancer therapy

BACKGROUND

New strategies are needed to improve the treatment of patients with breast cancer (BC). Oncolytic virotherapy is a promising new tool for cancer treatment but still has a limited overall durable antitumor response. A novel replicable recombinant oncolytic herpes simplex virus type 1 called VG161 has been developed and has demonstrated antitumor effects in several cancers. Here, we explored the efficacy and the antitumor immune response of VG161 cotreatment with paclitaxel (PTX) which as a novel oncolytic viral immunotherapy for BC.

METHODS

The antitumor effect of VG161 and PTX was confirmed in a BC xenograft mouse model. The immunostimulatory pathways were tested by RNA-seq and the remodeling of tumor microenvironment was detected by Flow cytometry analysis or Immunohistochemistry. Pulmonary lesions were analyzed by the EMT6-Luc BC model.

RESULTS

In this report, we demonstrate that VG161 can significantly represses BC growth and elicit a robust antitumor immune response in a mouse model. The effect is amplified when combined with PTX treatment. The antitumor effect is associated with the infiltration of lymphoid cells, including CD4⁺ T cells, CD8⁺ T cells, and NK cells (expressing TNF and IFN-γ), and myeloid cells, including macrophages, myeloid-derived suppressor cells, and dendritic cell cells. Additionally, VG161 cotreatment with PTX showed a significant reduction in BC lung metastasis, which may result from the enhanced CD4⁺ and CD8⁺ T cell-mediated responses.

CONCLUSIONS

The combination of PTX and VG161 is effective for repressing BC growth by inducing proinflammatory changes in the tumor microenvironment and reducing BC pulmonary metastasis. These data will provide a new strategy and valuable insight for oncolytic virus therapy applications in primary solid or metastatic BC tumors.

Engineered microorganism-based delivery systems for targeted cancer therapy: a narrative review

Microorganisms with innate and artificial advantages have been regarded as intelligent drug delivery systems for cancer therapy with the help of engineering technology. Although numerous studies have confirmed the promising prospects of microorganisms in cancer, several problems such as immunogenicity and toxicity should be addressed before further clinical applications. This review aims to investigate the development of engineered microorganism-based delivery systems for targeted cancer therapy. The main types of microorganisms such as bacteria, viruses, fungi, microalgae, and their components and characteristics are introduced in detail. Moreover, the engineering strategies and biomaterials design of microorganisms are further discussed. Most importantly, we discuss the innovative attempts and therapeutic effects of engineered microorganisms in cancer. Taken together, engineered microorganism-based delivery systems hold tremendous promise for biomedical applications in targeted cancer therapy.

Current clinical landscape of oncolytic viruses as novel cancer immunotherapeutic and recent preclinical advancements

Oncolytic viruses (OVs) have been gaining attention in the pharmaceutical industry as a novel immunotherapeutic and therapeutic adjuvant due to their ability to induce and boost antitumor immunity through multiple mechanisms. First, intrinsic mechanisms of OVs that enable exploitation of the host immune system (e.g., evading immune detection) can nullify the immune escape mechanism of tumors. Second, many types of OVs have been shown to cause direct lysis of tumor cells, resulting in an induction of tumor-specific T cell response mediated by release of tumor-associated antigens and danger signal molecules. Third, armed OV-expressing immune stimulatory therapeutic genes could be highly expressed in tumor tissues to further improve antitumor immunity. Last, these OVs can inflame cold tumors and their microenvironment to be more immunologically favorable for other immunotherapeutics. Due to these unique characteristics, OVs have been tested as an adjuvant of choice in a variety of therapeutics. In light of these promising attributes of OVs in the immune-oncology field, the present review will examine OVs in clinical development and discuss various strategies that are being explored in preclinical stages for the next generation of OVs that are optimized for immunotherapy applications.

Herpes simplex virus 1 as an oncolytic viral therapy for refractory cancers

The need for efficacious and non-toxic cancer therapies is paramount. Oncolytic viruses (OVs) are showing great promise and are introducing new possibilities in cancer treatment with their ability to selectively infect tumor cells and trigger antitumor immune responses. Herpes Simplex Virus 1 (HSV-1) is a commonly selected OV candidate due to its large genome, relative safety profile, and ability to infect a variety of cell types. Talimogene laherparevec (T-VEC) is an HSV-1-derived OV variant and the first and only OV therapy currently approved for clinical use by the United States Food and Drug Administration (FDA). This review provides a concise description of HSV-1 as an OV candidate and the genomic organization of T-VEC. Furthermore, this review focuses on the advantages and limitations in the use of T-VEC compared to other HSV-1 OV variants currently in clinical trials. In addition, approaches for future directions of HSV-1 OVs as cancer therapy is discussed.

Identification of Rab27a as a host factor for oncolytic herpes virus susceptibility to tumor cells

Oncolytic viruses are emerging as therapeutic agents in oncology. However, resistance of tumor cells to HSV oncolysis pose significant barriers to antitumor response. Thus, study on the mechanisms of therapeutic resistance to oHSV and finding strategies for overcoming these mechanisms are needed. In this study, Rab27a, a small GTPase involved in exosome biogenesis, was noticed to highly correlate with the susceptibility of tumor cells to oHSV. We found that i) lower abundance of Rab27a in oHSV resistant mouse tumor cells was shown when compared to that of sensitive tumor cells through deep-sequencing; ii) the resistance of human tumor cells to oHSV infection is associated with a downregulation of Rab27a expression and overexpression of Rab27a can promote the replication capacity of oHSV; iii) Interestingly, a stabilizer protein of Rab27a, KIBRA, highly accumulated in oHSV resistant tumor cells, which is in contrast with the expression pattern of Rab27a. Furthermore, knockdown of KIBRA expression reduced oHSV replication in oHSV resistant tumor cells. Consequently, Rab27a was found to be relevant with oHSV replication without cell type specificity, and low abundance of Rab27a contributes to oHSV resistance in both mouse and human tumor cells, which will give new insights in the identification of potential targets or biomarkers for oHSV cancer therapy.

Oncolytic herpes simplex virus infects myeloma cells in vitro and in vivo

Because most patients with multiple myeloma (MM) develop resistance to current regimens, novel approaches are needed. Genetically modified, replication-competent oncolytic viruses exhibit high tropism for tumor cells regardless of cancer stage and prior treatment. Receptors of oncolytic herpes simplex virus 1 (oHSV-1), NECTIN-1, and HVEM are expressed on MM cells, prompting us to investigate the use of oHSV-1 against MM. Using oHSV-1-expressing GFP, we found a dose-dependent increase in the GFP⁺ signal in MM cell lines and primary MM cells. Whereas NECTIN-1 expression is variable among MM cells, we discovered that HVEM is ubiquitously and highly expressed on all samples tested. Expression of HVEM was consistently higher on CD138⁺/CD38⁺ plasma cells than in non-plasma cells. HVEM blocking demonstrated the requirement of this receptor for infection. However, we observed that, although oHSV-1 could efficiently infect and kill all MM cell lines tested, no viral replication occurred. Instead, we identified that oHSV-1 induced MM cell apoptosis via caspase-3 cleavage. We further noted that oHSV-1 yielded a significant decrease in tumor volume in two mouse xenograft models. Therefore, oHSV-1 warrants exploration as a novel potentially effective treatment option in MM, and HVEM should be investigated as a possible therapeutic target.

Polytherapeutic strategies with oncolytic virus-bortezomib and adjuvant NK cells in cancer treatment

Proteasome inhibition and oncolytic virotherapy are two emerging targeted cancer therapies. Bortezomib, a proteasome inhibitor, disrupts the degradation of proteins in the cell leading to accumulation of unfolded proteins inducing apoptosis. On the other hand, oncolytic virotherapy uses genetically modified oncolytic viruses (OV) to infect cancer cells, induce cell lysis, and activate an antitumour response. In this work, optimal control theory is used to minimize the cancer cell population by identifying strategic infusion protocols of bortezomib, OV and natural killer (NK) cells. Three different therapeutic protocols are explored: (i) periodic bortezomib and single administrations of both OV and NK cells therapy; (ii) alternating sequential combination therapy; and (iii) NK cell depletion and infusion therapy. In the first treatment scheme, early OV administration followed by well-timed adjuvant NK cell infusion maximizes antitumour efficacy. The second strategy supports timely OV infusion. The last treatment scheme indicates that transient NK cell depletion followed by appropriate NK cell adjuvant therapy yields the maximal benefits. Relative doses and administrative costs of the three anticancer agents for each approach are qualitatively presented. This study provides potential polytherapeutic strategies in cancer treatment.

Synthesis of non-nucleoside anti-viral cyclopropylcarboxacyl hydrazones and initial anti-HSV-1 structure-activity relationship studies

The synthesis of a lead anti-viral cyclopropyl carboxy acyl hydrazone 4F17 (5) and three sequential arrays of structural analogues along with the initial assessment and optimization of the antiviral pharmacophore against the herpes simplex virus type 1 (HSV-1) are reported.

Eradicating the Roots: Advanced Therapeutic Approaches Targeting Breast Cancer Stem Cells

Accumulating evidences have demonstrated that the existence of breast cancer-initiating cells, which drives the original tumorigenicity, local invasion and migration propensity of breast cancer. These cells, termed as breast cancer stem cells (BCSCs), possess properties including self-renewal, multidirectional differentiation and proliferative potential, and are believed to play important roles in the intrinsic drug resistance of breast cancer. One of the reasons why BCBCs cause difficulties in breast cancer treating is that BCBCs can control both genetic and non-genetic elements to keep their niches safe and sound, which allows BCSCs for constant self-renewal and differentiation. Therapeutic strategies designed to target BCSCs may ultimately result in effective interventions for the treatment of breast cancer. Novel strategies including nanomedicine, oncolytic virus therapy, immunotherapy and induced differentiation therapy are emerging and proved to be efficient in anti-BCSCs therapy. In this review, we summarized breast tumor biology and the current challenges of breast cancer therapies, focused on breast cancer stem cells, and introduced promising therapeutic strategies targeting BCSCs.

Oncolytic Virotherapy for Malignant Tumor: Current Clinical Status

Oncolytic viruses, as novel biological anti-tumor agents, provide anti-tumor therapeutic effects by different mechanisms including directly selective tumor cell lysis and secondary systemic anti-tumor immune responses. Some wide-type and genetically engineered oncolytic viruses have been applied in clinical trials. Among them, T-Vec has a significant therapeutic effect on melanoma patients and received the approval of the US Food and Drug Administration (FDA) as the first oncolytic virus to treat cancer in the US. However, the mechanisms of virus interaction with tumor and immune systems have not been clearly elucidated and there are still no "gold standards" for instructions of virotherapy in clinical trials. This Review collected the recent clinical trials data from 2005 to summarize the basic oncolytic viruses biology, describe the application in recent clinical trials, and discuss the challenges in the application of oncolytic viruses in clinical trials.

Oncolytic Herpes Simplex Virus and PI3K Inhibitor BKM120 Synergize to Promote Killing of Prostate Cancer Stem-like Cells

Novel therapies to override chemo-radiation resistance in prostate cancer (PCa) are needed. Prostate cancer sphere-forming cells (PCSCs) (also termed prostate cancer stem-like cells) likely participate in tumor progression and recurrence, and they are important therapeutic targets. We established PCSC-enriched spheres by culturing human (DU145) and murine (TRAMP-C2) PCa cells in growth factor-defined serum-free medium, and we characterized stem-like properties of clonogenicity and tumorigenicity. The efficacy of two different oncolytic herpes simplex viruses (oHSVs) (G47Δ and MG18L) in PCSCs was tested alone and in combination with radiation; chemotherapy; and inhibitors of phosphoinositide 3-kinase (PI3K), Wnt, and NOTCH in vitro; and, G47Δ was tested with the PI3K inhibitor BKM120 in a PCSC-derived tumor model in vivo. PCSCs were more tumorigenic than serum-cultured parental cells. Human and murine PCSCs were sensitive to oHSV and BKM120 killing in vitro, while the combination was synergistic. oHSV combined with radiation, docetaxel, Wnt, or NOTCH inhibitors was not. In athymic mice bearing DU145 PCSC-derived tumors, the combination of intra-tumoral G47Δ and systemic BKM120 induced complete regression of tumors in 2 of 7 animals, and it exhibited superior anti-tumor activity compared to either monotherapy alone, with no detectable toxicity. oHSV synergizes with BKM120 in killing PCSCs in vitro, and the combination markedly inhibits tumor growth, even inducing regression in vivo.

Oncolytic herpes simplex virus and immunotherapy

BACKGROUND

Oncolytic viruses have been proposed to be employed as a potential treatment of cancer. Well targeted, they will serve the purpose of cracking tumor cells without causing damage to normal cells. In this category of oncolytic viral drugs human pathogens herpes simplex virus (HSV) is especially suitable for the cause. Although most viral infection causes antiviral reaction in the host, HSV has multiple mechanisms to evade those responses. Powerful anti-tumor effect can thus be achieved via genetic manipulation of the HSV genes involved in this evading mechanism, namely deletions or mutations that adapt its function towards a tumor microenvironment. Currently, oncolytic HSV (oHSV) is widely use in clinical; moreover, there's hope that its curative effect will be further enhanced through the combination of oHSV with both traditional and emerging therapeutics.

RESULTS

In this review, we provide a summary of the HSV host antiviral response evasion mechanism, HSV expresses immune evasion genes such as ICP34.5, ICP0, Us3, which are involved in inducing and activating host responses, so that the virus can evade the immune system and establish effective long-term latent infection; we outlined details of the oHSV strains generated by removing genes critical to viral replication such as ICP34.5, ICP0, and inserting therapeutic genes such as LacZ, granulocyte macrophage colony-stimulating factor (GM-CSF); security and limitation of some oHSV such G207, 1716, OncoVEX, NV1020, HF10, G47 in clinical application; and the achievements of oHSV combined with immunotherapy and chemotherapy.

CONCLUSION

We reviewed the immunotherapy mechanism of the oHSV and provided a series of cases. We also pointed out that an in-depth study of the application of oHSV in cancer treatment will potentially benefits cancer patients more.

Please stand by: how oncolytic viruses impact bystander cells

Oncolytic viruses (OVs) do more than simply infect and kill host cells. The accepted mechanism of action for OVs consists of a primary lytic phase and a subsequent antitumor and antiviral immune response. However, not all cells are subject to the direct effects of OV therapy, and it is becoming clear that OVs can also impact uninfected cells in the periphery. This review discusses the effects of OVs on uninfected neighboring cells, so-called bystander effects, and implications for OV therapies alone or in combination with other standard of care chemotherapy.

Complex role of NK cells in regulation of oncolytic virus-bortezomib therapy

In the present work, we investigated the role of natural killer (NK) cells in combination therapy with oncolytic virus (OV) and bortezomib, a proteasome inhibitor. NK cells display rapid and potent immunity to metastatic and hematological cancers, and they overcome immunosuppressive effects of tumor microenvironment. We developed a mathematical model to address the question of how the density of NK cells affects the growth of the tumor. We found that the antitumor efficacy increases when the endogenous NKs are depleted and also when exogenous NK cells are injected into the tumor. These predictions were validated by our in vivo and in vitro experiments.

High Mobility Group Box 1 Influences HSV1716 Spread and Acts as an Adjuvant to Chemotherapy

High Mobility Group Box 1 (HMGB1) is a multifunctional protein that plays various roles in the processes of inflammation, cancer, and other diseases. Many reports document abundant HMGB1 release following infection with oncolytic viruses (OVs). Further, other groups including previous reports from our laboratory highlight the synergistic effects of OVs with chemotherapy drugs. Here, we show that virus-free supernatants have varying cytotoxic potential, and HMGB1 is actively secreted by two established fibroblast cell lines (NIH 3T3 and 3T6-Swiss albino) following HSV1716 infection in vitro. Further, pharmacologic inhibition or genetic knock-down of HMGB1 reveals a role for HMGB1 in viral restriction, the ability to modulate bystander cell proliferation, and drug sensitivity in 3T6 cells. These data further support the multifactorial role of HMGB1, and suggest it could be a target for modulating the efficacy of oncolytic virus therapies alone or in combination with other frontline cancer treatments.

Bortezomib Treatment Sensitizes Oncolytic HSV-1-Treated Tumors to NK Cell Immunotherapy

PURPOSE

Both the proteasome inhibitor bortezomib and an oncolytic herpes simplex virus-1 (oHSV)-expressing GM-CSF are currently FDA approved. Although proteasome blockade can increase oHSV replication, immunologic consequences, and consequent immunotherapy potential are unknown. In this study, we investigated the impact of bortezomib combined with oHSV on tumor cell death and sensitivity to natural killer (NK) cell immunotherapy.

EXPERIMENTAL DESIGN

Western blot, flow cytometry, and caspase 3/7 activity assays were used to evaluate the induction of apoptosis/autophagy and/or necroptotic cell death. Cellular and mitochondrial reactive oxygen species (ROS) production was measured using CellROX and MitoSOX. Inhibitors/shRNA-targeting ROS, JNK and RIP1 kinase (RIPK1) were used to investigate the mechanism of cell killing. The synergistic interaction between oHSV and bortezomib was calculated using a Chou-Talalay analysis. NK cells isolated from normal human blood were co-cultured with tumor cells to evaluate cellular interactions. Q-PCR, ELISA, and FACS analysis were used to evaluate NK cell activation. Intracranial tumor xenografts were used to evaluate antitumor efficacy.

RESULTS

Combination treatment with bortezomib- and oHSV-induced necroptotic cell death and increased the production of mitochondrial ROS and JNK phosphorylation. Inhibitors/shRNA of RIPK1 and JNK rescued synergistic cell killing. Combination treatment also significantly enhanced NK cell activation and adjuvant NK cell therapy of mice treated with bortezomib and oHSV improved antitumor efficacy.

CONCLUSIONS

This study provides a significant rationale for triple combination therapy with bortezomib, oHSV, and NK cells to improve efficacy, in glioblastoma patients. Clin Cancer Res; 22(21); 5265-76. ©2016 AACRSee related commentary by Suryadevara et al., p. 5164.

Unlocking the promise of oncolytic virotherapy in glioma: combination with chemotherapy to enhance efficacy

Malignant glioma is a relentless burden to both patients and clinicians, and calls for innovation to overcome the limitations in current management. Glioma therapy using viruses has been investigated to accentuate the nature of a virus, killing a host tumor cell during its replication. As virus mediated approaches progress with promising therapeutic advantages, combination therapy with chemotherapy and oncolytic viruses has emerged as a more synergistic and possibly efficacious therapy. Here, we will review malignant glioma as well as prior experience with oncolytic viruses, chemotherapy and combination of the two, examining how the combination can be optimized in the future.

Prospect and progress of oncolytic viruses for treating peripheral nerve sheath tumors

INTRODUCTION

Peripheral nerve sheath tumors (PNSTs) are an assorted group of neoplasms originating from neuroectoderm and growing in peripheral nerves. Malignant transformation leads to a poor prognosis and is often lethal. Current treatment of PNSTs is predominantly surgical, which is often incomplete or accompanied by significant loss of function, in conjunction with radiotherapy and/or chemotherapy, for which the benefits are inconclusive. Oncolytic viruses (OVs) efficiently kill tumor cells while remaining safe for normal tissues, and are a novel antitumor therapy for patients with PNSTs.

AREAS COVERED

Because of the low efficacy of current treatments, new therapies for PNSTs are needed. Pre-clinically, OVs have demonstrated efficacy in treating PNSTs and perineural tumor invasion, as well as safety. We will discuss the various PNSTs and their preclinical models, and the OVs being tested for their treatment, including oncolytic herpes simplex virus (HSV), adenovirus (Ad), and measles virus (MV). OVs can be 'armed' to express therapeutic transgenes or combined with other therapeutics to enhance their activity.

EXPERT OPINION

Preclinical testing of OVs in PNST models has demonstrated their therapeutic potential and provided support for clinical translation. Clinical studies with other solid tumors have provided evidence that OVs are safe in patients and efficacious. The recent successful completion of a phase III clinical trial of oncolytic HSV paves the way for oncolytic virotherapy to enter clinical practice.

Designing Herpes Viruses as Oncolytics

Oncolytic herpes simplex virus (oHSV) was one of the first genetically-engineered oncolytic viruses. Because herpes simplex virus (HSV) is a natural human pathogen that can cause serious disease, it is incumbent that it be genetically-engineered or significantly attenuated for safety. Here we present a detailed explanation of the functions of HSV-1 genes frequently mutated to endow oncolytic activity. These genes are non-essential for growth in tissue culture cells but are important for growth in post-mitotic cells, interfering with intrinsic antiviral and innate immune responses or causing pathology, functions dispensable for replication in cancer cells. Understanding the function of these genes leads to informed creation of new oHSVs with better therapeutic efficacy. Virus infection and replication can also be directed to cancer cells through tumor-selective receptor binding and transcriptional- or post-transcriptional miRNA-targeting, respectively. In addition to the direct effects of oHSV on infected cancer cells and tumors, oHSV can be 'armed' with transgenes that are: reporters, to track virus replication and spread; cytotoxic, to kill uninfected tumor cells; immune modulatory, to stimulate anti-tumor immunity; or tumor microenvironment altering, to enhance virus spread or to inhibit tumor growth. In addition to HSV-1, other alphaherpesviruses are also discussed for their oncolytic activity.

Promising oncolytic agents for metastatic breast cancer treatment

New therapies for metastatic breast cancer patients are urgently needed. The long-term survival rates remain unacceptably low for patients with recurrent disease or disseminated metastases. In addition, existing therapies often cause a variety of debilitating side effects that severely impact quality of life. Oncolytic viruses constitute a developing therapeutic modality in which interest continues to build due to their ability to spare normal tissue while selectively destroying tumor cells. A number of different viruses have been used to develop oncolytic agents for breast cancer, including herpes simplex virus, adenovirus, vaccinia virus, measles virus, reovirus, and others. In general, clinical trials for several cancers have demonstrated excellent safety records and evidence of efficacy. However, the impressive tumor responses often observed in preclinical studies have yet to be realized in the clinic. In order for the promise of oncolytic virotherapy to be fully realized for breast cancer patients, effectiveness must be demonstrated in metastatic disease. This review provides a summary of oncolytic virotherapy strategies being developed to target metastatic breast cancer.

Combinatorial strategies for oncolytic herpes simplex virus therapy of brain tumors

Oncolytic viruses, such as the oncolytic herpes simplex virus (oHSV), are an exciting new therapeutic strategy for cancer as they are replication competent in tumor cells but not normal cells. In order to engender herpes simplex virus with oncolytic activity and make it safe for clinical application, mutations are engineered into the virus. Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor in adults. Despite many advances in therapy, overall survival has not been substantially improved over the last several decades. A number of different oHSVs have been tested as monotherapy in early-phase clinical trials for GBM and have demonstrated safety and anecdotal evidence of efficacy. However, strategies to improve efficacy are likely to be necessary to successfully treat GBM. Cancer treatment usually involves multimodal approaches, so the standard of care for GBM includes surgery, radiotherapy and chemotherapy. In preclinical GBM models, combinations of oHSV with other types of therapy have exhibited markedly improved activity over individual treatments alone. In this review, we will discuss the various combination strategies that have been employed with oHSV, including chemotherapy, small-molecule inhibitors, antiangiogenic agents, radiotherapy and expression of therapeutic transgenes. Effective combinations, especially synergistic ones, are clinically important not just for improved efficacy but also to permit lower and less-toxic doses and potentially overcome resistance.

Enhanced efficacy with azacytidine and oncolytic BHV-1 in a tolerized cotton rat model of breast adenocarcinoma

Oncolytic viruses selectively replicate in cancer cells by exploiting biochemical differences between normal and tumor cells. Treatment with epigenetic modifiers such as 5-Azacytidine, a DNA methyltransferase inhibitor, increases the replication and cytotoxicity of oncolytic viruses in vivo and in vitro. The cotton rat is an attractive animal to study oncolytic viruses, as syngeneic models of breast adenocarcinoma and osteosarcoma are well established, and many features of primary and secondary tumor growth recapitulate human disease. Treatment of LCRT breast cancer cells with 5-Azacytidine increases bovine herpesvirus type 1 (BHV-1)-mediated cytotoxicity in vitro, with Chou-Talalay analysis indicating a very strong synergy. In vivo, BHV-1 monotherapy delayed tumor growth but did not improve survival of cotton rats with subcutaneous breast adenocarcinomas. However, combination therapy significantly decreased the incidence of secondary lesions, with enhanced tumor cell clearance and evidence of immune cell infiltration compared to BHV-1 monotherapy. Together, these results warrant further investigation of BHV-1 combination therapy with epigenetic modifiers for the treatment of breast cancer, particularly in the context of the prevention and treatment of secondary lesions.

Chemovirotherapy: combining chemotherapeutic treatment with oncolytic virotherapy

Oncolytic virotherapy has made significant progress in recent years, however, widespread approval of virotherapeutics is still limited. Primarily, this is due to the fact that currently available virotherapeutics are mostly tested in monotherapeutic clinical trials exclusively (ie, not in combination with other therapies) and so far have achieved only small and often clinically insignificant responses. Given that the predominantly immunotherapeutic mechanism of virotherapeutics is somewhat time-dependent and rapidly growing tumors therefore exhibit only minor chances of being captured in time, scenarios with combination partners are postulated to be more effective. Combinatory settings would help to achieve a rapid stabilization or even reduction of onset tumor masses while providing enough time (numerous months) for achieving immuno(viro)therapeutic success. For this reason, combination strategies of virotherapy with highly genotoxic regimens, such as chemotherapy, are of major interest. A number of clinical trials bringing the concepts of chemotherapy and virotherapy together have previously been undertaken, but optimal scheduling of chemovirotherapy (maximizing the anti-tumor effect while minimizing the risk of overlapping toxicity) still constitutes a major challenge. Therefore, an overview of published as well as ongoing Phase I–III trials should improve our understanding of current challenges and future developments in this field.

Bortezomib-induced unfolded protein response increases oncolytic HSV-1 replication resulting in synergistic antitumor effects

BACKGROUND

Bortezomib is an FDA-approved proteasome inhibitor, and oncolytic herpes simplex virus-1 (oHSV) is a promising therapeutic approach for cancer. We tested the impact of combining bortezomib with oHSV for antitumor efficacy.

EXPERIMENTAL DESIGN

The synergistic interaction between oHSV and bortezomib was calculated using Chou-Talalay analysis. Viral replication was evaluated using plaque assay and immune fluorescence. Western blot assays were used to evaluate induction of estrogen receptor (ER) stress and unfolded protein response (UPR). Inhibitors targeting Hsp90 were utilized to investigate the mechanism of cell killing. Antitumor efficacy in vivo was evaluated using subcutaneous and intracranial tumor xenografts of glioma and head and neck cancer. Survival was analyzed by Kaplan-Meier curves and two-sided log-rank test.

RESULTS

Combination treatment with bortezomib and oHSV (34.5ENVE), displayed strong synergistic interaction in ovarian cancer, head and neck cancer, glioma, and malignant peripheral nerve sheath tumor (MPNST) cells. Bortezomib treatment induced ER stress, evident by strong induction of Grp78, CHOP, PERK, and IRE1α (Western blot analysis) and the UPR (induction of hsp40, 70, and 90). Bortezomib treatment of cells at both sublethal and lethal doses increased viral replication (P < 0.001), but inhibition of Hsp90 ablated this response, reducing viral replication and synergistic cell killing. The combination of bortezomib and 34.5ENVE significantly enhanced antitumor efficacy in multiple different tumor models in vivo.

CONCLUSIONS

The dramatic synergy of bortezomib and 34.5ENVE is mediated by bortezomib-induced UPR and warrants future clinical testing in patients.

Histone deacetylase inhibitors improve the replication of oncolytic herpes simplex virus in breast cancer cells

New therapies are needed for metastatic breast cancer patients. Oncolytic herpes simplex virus (oHSV) is an exciting therapy being developed for use against aggressive tumors and established metastases. Although oHSV have been demonstrated safe in clinical trials, a lack of sufficient potency has slowed the clinical application of this approach. We utilized histone deacetylase (HDAC) inhibitors, which have been noted to impair the innate antiviral response and improve gene transcription from viral vectors, to enhance the replication of oHSV in breast cancer cells. A panel of chemically diverse HDAC inhibitors were tested at three different doses (<,  = , and >LD50) for their ability to modulate the replication of oHSV in breast cancer cells. Several of the tested HDAC inhibitors enhanced oHSV replication at low multiplicity of infection (MOI) following pre-treatment of the metastatic breast cancer cell line MDA-MB-231 and the oHSV-resistant cell line 4T1, but not in the normal breast epithelial cell line MCF10A. Inhibitors of class I HDACs, including pan-selective compounds, were more effective for increasing oHSV replication compared to inhibitors that selectively target class II HDACs. These studies demonstrate that select HDAC inhibitors increase oHSV replication in breast cancer cells and provides support for pre-clinical evaluation of this combination strategy.

Tat-PTD-modified oncolytic adenovirus driven by the SCG3 promoter and ASH1 enhancer for neuroblastoma therapy

Secretogranin III (SGC3) belongs to the granin family and is highly expressed in endocrine and neural tissues. The human SCG3 promoter has not yet been characterized. We identified that a 0.5-kb DNA fragment upstream of the SCG3 gene can selectively drive transgene expression in neuroblastoma cell lines. The strength of transgene expression was further increased, with specificity maintained, by addition of the human achaete-scute complex homolog 1 (ASH1) enhancer. We developed an oncolytic serotype 5-based adenovirus, in which the SCG3 promoter and ASH1 enhancer drive E1A gene expression. The virus was further modified with a cell-penetrating peptide (Tat-PTD) in the viral capsid, which we have previously shown results in increased adenovirus transduction efficiency of many neuroblastoma cell lines. The virus, Ad5PTD(ASH1-SCG3-E1A), shows selective and efficient killing of neuroblastoma cell lines in vitro, including cisplatin-, etoposide-, and doxorubicin-insensitive neuroblastoma cells. Furthermore, it delays tumor growth and thereby prolonged survival for nude mice harboring subcutaneous human neuroblastoma xenograft. In conclusion, we report a novel oncolytic adenovirus with potential use for neuroblastoma therapy.

Combination of oncolytic herpes simplex viruses armed with angiostatin and IL-12 enhances antitumor efficacy in human glioblastoma models

Oncolytic herpes simplex virus (oHSV) can potentially spread throughout the tumor, reach isolated infiltrating cells, kill them, and deliver anticancer agents. However, the host responds to oHSV by inducing intratumoral infiltration of macrophages that can engulf the virus, limiting the potential of this therapeutic strategy. Hypervascularity is a pathognomonic feature of glioblastoma (GBM) and is a promising therapeutic target. Antiangiogenic treatments have multiple benefits, including the capacity to increase oHSV efficacy by suppressing macrophage extravasation and infiltration into the tumor. Angiostatin is an antiangiogenic polypeptide, and interleukin-12 (IL-12) is an immunostimulatory cytokine with strong antiangiogenic effects. Clinical use of each has been limited by delivery issues and systemic toxicity. We tested a combination treatment strategy using oHSVs expressing angiostatin (G47Δ-mAngio) and IL-12 (G47Δ-mIL12) in two orthotopic human GBM models. Intratumoral injection of G47Δ-mAngio and G47Δ-mIL12 in mice bearing intracranial U87 or tumors derived from glioblastoma stem cells significantly prolonged survival compared to each armed oHSV alone. This was associated with increased antiangiogenesis and virus spread and decreased macrophages. These data support the paradigm of using oHSV expressing different antiangiogenic agents and show for the first time that oHSVs expressing angiostatin and IL-12 can improve efficacy in human GBM models.

Combining oncolytic HSV-1 with immunogenic cell death-inducing drug mitoxantrone breaks cancer immune tolerance and improves therapeutic efficacy

Although antitumor activity of herpes simplex virus 1 (HSV-1) ICP0 null oncolytic vectors has been validated in murine breast cancer models, oncolytic virus treatment alone is insufficient to break immune tolerance. Thus, we investigated enhancing efficacy through combination therapy with the immunogenic cell death-inducing chemotherapeutic drug, mitoxantrone. Despite a lack of enhanced cytotoxicity in vitro, HSV-1 ICP0 null oncolytic virus KM100 with 5 μmol/L mitoxantrone provided significant survival benefit to BALB/c mice bearing Her2/neu TUBO-derived tumors. This protection was mediated by increased intratumoral infiltration of neutrophils and tumor antigen-specific CD8(+) T cells. Depletion studies verified that CD8-, CD4-, and Ly6G-expressing cells are essential for enhanced efficacy of the combination therapy. Moreover, the addition of mitoxantrone to KM100 oncolytic virus treatment broke immune tolerance in BALB-neuT mice bearing TUBO-derived tumors. This study suggests that oncolytic viruses in combination with immunogenic cell death-inducing chemotherapeutics enhance the immunogenicity of the tumor-associated antigens, breaking immunologic tolerance established toward these antigens.

Advance in herpes simplex viruses for cancer therapy

Oncolytic virotherapy is an attractive approach that uses live viruses to selectively kill cancer cells. Oncolytic viruses can be genetically engineered to induce cell lyses through virus replication and cytotoxic protein expression. Herpes simplex virus (HSV) has become one of the most widely clinically used oncolytic agent. Various types of HSV have been studied in basic or clinical research. Combining oncolytic virotherapy with chemotherapy or radiotherapy generally produces synergic action with unclear molecular mechanisms. Arming HSV with therapeutic transgenes is a promising strategy and can be used to complement conventional therapies. As an efficient gene delivery system, HSV has been successfully used to deliver various immunomodulatory molecules. Arming HSV with therapeutic genes merits further investigation for potential clinical application.

Doxorubicin-enriched, ALDH(br) mouse breast cancer stem cells are treatable to oncolytic herpes simplex virus type 1

BACKGROUND

The primary objective of this study was to test whether oncolytic herpes simplex virus type 1 (HSV1) could eradicate chemoresistant cancer stem cells (CSCs).

METHODS

The fluorescent aldefluor reagent-based technique was used to identify and isolate ALDH(br) cells as CSCs from the 4T1 murine breast cancer cell line. The presence of ALDH(br) 4T1 cells was also examined in 4T1 breast cancer transplanted in immune-competent syngeneic mice.

RESULTS

Compared with ALDH(lo) cells, ALDH(br) cells had a markedly higher ability to form tumor spheres in vitro and a higher tumorigenic potential in vivo. ALDH(br) cells also exhibited increased doxorubicin resistance in vitro, which correlated with a selective increase in the percentage of ALDH(br) cells after doxorubicin treatment and an increased expression of P-glycoprotein (P-gp), a known chemoresistance factor. In contrast, oncolytic HSV1 was able to kill ALDH(br) cells in vitro and even more markedly in vivo. Furthermore, in in vivo studies, systemic administration of doxorubicin followed by intratumoral injection of oncolytic HSV1 resulted in much more significant suppression of tumor growth with increased median survival period compared with each treatment given alone (p<0.05). Though more CD8(+) T lymphocytes were induced by oncolytic HSV1, no significant specific T cell response against CSCs was detected in vivo.

CONCLUSIONS

These results suggested that the use of oncolytic HSV1 following doxorubicin treatment may help eradicate residual chemoresistant CSCs in vivo.

Progress of oncolytic viruses in sarcomas

Oncolytic virotherapy has shown exciting promise for the treatment of many types of solid tumors. Pediatric sarcomas are an aggressive type of pediatric malignancy known to show limited responsiveness to current therapies, leading to unacceptably high morbidity and mortality. Oncolytic viruses have only recently been used for the treatment of this challenging cancer, and results have been encouraging. Five clinical trials are currently open evaluating the use of oncolytic viruses in pediatric malignancies. Advances in genetic engineering of the viruses include improving the ability of the virus to infect tumor cells, engineering the virus with transgenes which improve the virus' ability to kill tumor cells and manipulating the virus to enhance concomitantly administered therapies. Further understanding of the antiviral immune response and a viral induced anti-tumor immune response will permit a maximization of oncolytic virotherapy.

Oncolytic virotherapy

Oncolytic virotherapy is an emerging treatment modality that uses replication-competent viruses to destroy cancers. Recent advances include preclinical proof of feasibility for a single-shot virotherapy cure, identification of drugs that accelerate intratumoral virus propagation, strategies to maximize the immunotherapeutic action of oncolytic viruses and clinical confirmation of a critical viremic threshold for vascular delivery and intratumoral virus replication. The primary clinical milestone has been completion of accrual in a phase 3 trial of intratumoral herpes simplex virus therapy using talimogene laherparepvec for metastatic melanoma. Key challenges for the field are to select 'winners' from a burgeoning number of oncolytic platforms and engineered derivatives, to transiently suppress but then unleash the power of the immune system to maximize both virus spread and anticancer immunity, to develop more meaningful preclinical virotherapy models and to manufacture viruses with orders-of-magnitude higher yields than is currently possible.

Virus-mediated gene delivery for human gene therapy

After over 20 years from the first application of gene transfer in humans, gene therapy is now a mature discipline, which has progressively overcome several of the hurdles that prevented clinical success in the early stages of application. So far, the vast majority of gene therapy clinical trials have exploited viral vectors as very efficient nucleic acid delivery vehicles both in vivo and ex vivo. Here we summarize the current status of viral gene transfer for clinical applications, with special emphasis on the molecular properties of the major classes of viral vectors and the information so far obtained from gene therapy clinical trials.

In vivo evaluation of a cancer therapy strategy combining HSV1716-mediated oncolysis with gene transfer and targeted radiotherapy

Oncolytic herpes viruses show promise for cancer treatment. However, it is unlikely that they will fulfill their therapeutic potential when used as monotherapies. An alternative strategy is to use these viruses not only as oncolytic agents but also as a delivery mechanism of therapeutic transgenes to enhance tumor cell killing. The herpes simplex virus 1 deletion mutant HSV1716 is a conditionally replicating oncolytic virus that selectively replicates in and lyses dividing tumor cells. It has a proven safety profile in clinical trials and has demonstrated efficacy as a gene-delivery vehicle. To enhance its therapeutic potential, we have engineered HSV1716 to convey the noradrenaline transporter (NAT) gene (HSV1716/NAT), whose expression endows infected cells with the capacity to accumulate the noradrenaline analog metaiodobenzylguanidine (MIBG). Thus, the NAT gene-infected cells are susceptible to targeted radiotherapy using radiolabeled (131)I-MIBG, a strategy that has already shown promise for combined targeted radiotherapy-gene therapy in cancer cells after plasmid-mediated transfection.

METHODS

We used HSV1716/NAT as a dual cell lysis-gene delivery vehicle for targeting the NAT transgene to human tumor xenografts in vivo.

RESULTS

In tumor xenografts that did not express NAT, intratumoral or intravenous injection of HSV1716/NAT induced the capacity for active uptake of (131)I-MIBG. Administration of HSV1716/NAT and (131)I-MIBG resulted in decreased tumor growth and enhanced survival relative to injection of either agent alone. Efficacy was dependent on the scheduling of delivery of the 2 agents.

CONCLUSION

These findings support a role for combination radiotherapy-gene therapy for cancer using HSV1716 expressing the NAT transgene and targeted radionuclide therapy.

RNAi knockdown of the Akt1 gene increases the chemosensitivity of gastric cancer cells to cisplatin both in vitro and in vivo

AIM

To examine the in vitro and in vivo effects of a combined treatment of cis-d iamminedichloroplatinum(II) (cisplatin) with downregulation of Akt1 expression in gastric cancer cells.

MATERIALS AND METHODS

Lentivirus-mediated RNA interference (RNAi) was used to silence the Akt1 gene. pGCSIL-Akt1 small hairpin RNA (shRNA) was stably transfected into gastric cancer cells (SGC7901 and BGC823). Next, the effects of Akt1 downregulation on the growth and apoptosis of SGC7901 (BGC823) cells in the presence or absence of cisplatin were investigated by real-time polymerase chain reaction (RT-PCR), Western blot analysis, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-d-iphenyltetrazolium bromide) assay, Hoechst assay, flow cytometric analysis of annexin V-FITC/PI staining, and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling). Finally, the effects of downregulation of Akt1 expression on the sensitivity of SGC7901 cells in a tumor xenograft model of cisplatin were also determined.

RESULT

Akt1 silencing reduced gastric cancer proliferation and increased cell apoptosis both in vitro and in vivo. The chemosensitivity of SGC7901 (BGC823) cells to cisplatin increased significantly following the downregulation of Akt1 expression, which might be associated with the inactivation of the PI3K/Akt1 signaling pathway, followed by the induced expression of the pro-apoptotic protein Bax and a concomitant decrease of Bcl-2 expression.

CONCLUSION

This study confirmed that downregulation of Akt1 reduced chemotherapy tolerance of gastric cancer cells to cisplatin treatment. Thus, Akt1 silencing and cisplatin appear to be an effective combination treatment strategy for gastric cancer.

Preferential replication of systemically delivered oncolytic vaccinia virus in focally irradiated glioma xenografts

PURPOSE

Radiotherapy is part of the standard of care in high-grade gliomas but its outcomes remain poor. Integrating oncolytic viruses with standard anticancer therapies is an area of active investigation. The aim of this study was to determine how tumor-targeted ionizing radiation (IR) could be combined with systemically delivered oncolytic vaccinia virus.

EXPERIMENTAL DESIGN

U-87 glioma xenografts were grown subcutaneously or orthotopically. Oncolytic vaccinia viruses GLV-1h68 and LIVP 1.1.1 were injected systemically and IR was given focally to glioma xenografts. In a bilateral tumor model, glioma xenografts were grown in both flanks, oncolytic vaccinia was injected systemically and radiation was delivered specifically to the right flank tumor, whereas the left flank tumor was shielded. Viral replication and tumor regression, after systemic injection, was analyzed and compared in irradiated and nonirradiated glioma xenografts.

RESULTS

Systemically administered oncolytic vaccinia virus replicated to higher titers in preirradiated U-87 xenografts than in nonirradiated glioma xenografts. This increased oncolytic viral replication correlated with increased tumor xenograft regression and mouse survival in subcutaneous and orthotopic U-87 glioma models compared with monotherapies. The ability of focal IR to mediate selective replication of oncolytic vaccinia was shown in a bilateral glioma model in which systemically administered oncolytic vaccinia replicated preferentially in the irradiated tumor compared with the nonirradiated tumor in the same mouse.

CONCLUSION

These findings show a potential clinical role of focal IR in sensitizing irradiated tumor sites for preferential vaccinia virus-mediated oncolysis.

Combination of a fusogenic glycoprotein, pro-drug activation and oncolytic HSV as an intravesical therapy for superficial bladder cancer

Background:

There are still no effective treatments for superficial bladder cancer (SBC)/non-muscle invasive bladder cancer. Following treatment, 20% of patients still develop metastatic disease. Superficial bladder cancer is often multifocal, has high recurrences after surgical resection and recurs after intravesical live Bacillus Calmette–Guérin. Oncovex^GALV/CD, an oncolytic herpes simplex virus-1, has shown enhanced local tumour control by combining oncolysis with the expression of a highly potent pro-drug activating gene and the fusogenic glycoprotein.

Methods:

In vitro fusion/prodrug/apoptotic cell-based assays. In vivo orthotopic bladder tumour model, visualised by computed microtomography.

Results:

Treatment of seven human bladder carcinoma cell lines with the virus resulted in tumour cell killing through oncolysis, pro-drug activation and glycoprotein fusion. Oncovex^GALV/CD and mitomycin C showed a synergistic effect, whereas the co-administration with cisplatin or gemcitabine showed an antagonistic effect in vitro. Transitional cell cancer (TCC) cells follow an apoptotic cell death pathway after infection with Oncovex^GALV/CD with or without 5-FC. In vivo results showed that intravesical treatment with Oncovex^GALV/CD + prodrug (5-FC) reduced the average tumour volume by over 95% compared with controls.

Discussion:

Our in vitro and in vivo results indicate that Oncovex^GALV/CD can improve local tumour control within the bladder, and potentially alter its natural history.

Oncolytic virus-mediated manipulation of DNA damage responses: synergy with chemotherapy in killing glioblastoma stem cells

BACKGROUND

Although both the alkylating agent temozolomide (TMZ) and oncolytic viruses hold promise for treating glioblastoma, which remains uniformly lethal, the effectiveness of combining the two treatments and the mechanism of their interaction on cancer stem cells are unknown.

METHODS

We investigated the efficacy of combining TMZ and the oncolytic herpes simplex virus (oHSV) G47Δ in killing glioblastoma stem cells (GSCs), using Chou-Talalay combination index analysis, immunocytochemistry and fluorescence microscopy, and neutral comet assay. The role of treatment-induced DNA double-strand breaks, activation of DNA damage responses, and virus replication in the cytotoxic interaction between G47Δ and TMZ was examined with a panel of pharmacological inhibitors and short-hairpin RNA (shRNA)-mediated knockdown of DNA repair pathways. Comparisons of cell survival and virus replication were performed using a two-sided t test (unpaired). The survival of athymic mice (n = 6-8 mice per group) bearing GSC-derived glioblastoma tumors treated with the combination of G47Δ and TMZ was analyzed by the Kaplan-Meier method and evaluated with a two-sided log-rank test.

RESULTS

The combination of G47Δ and TMZ acted synergistically in killing GSCs but not neurons, with associated robust induction of DNA damage. Pharmacological and shRNA-mediated knockdown studies suggested that activated ataxia telangiectasia mutated (ATM) is a crucial mediator of synergy. Activated ATM relocalized to HSV DNA replication compartments where it likely enhanced oHSV replication and could not participate in repairing TMZ-induced DNA damage. Sensitivity to TMZ and synergy with G47Δ decreased with O(6)-methylguanine-DNA-methyltransferase (MGMT) expression and MSH6 knockdown. Combined G47Δ and TMZ treatment extended survival of mice bearing GSC-derived intracranial tumors, achieving long-term remission in four of eight mice (median survival = 228 days; G47Δ alone vs G47Δ + TMZ, hazard ratio of survival = 7.1, 95% confidence interval = 1.9 to 26.1, P = .003) at TMZ doses attainable in patients.

CONCLUSIONS

The combination of G47Δ and TMZ acts synergistically in killing GSCs through oHSV-mediated manipulation of DNA damage responses. This strategy is highly efficacious in representative preclinical models and warrants clinical translation.

Enhanced antitumor efficacy of low-dose Etoposide with oncolytic herpes simplex virus in human glioblastoma stem cell xenografts

PURPOSE

Glioblastoma (GBM) inevitably recurs despite surgery, radiation, and chemotherapy. A subpopulation of tumor cells, GBM stem cells (GSC), has been implicated in this recurrence. The chemotherapeutic agent etoposide is generally reserved for treating recurrent tumors; however, its effectiveness is limited due to acute and cumulative toxicities to normal tissues. We investigate a novel combinatorial approach of low-dose etoposide with an oncolytic HSV to enhance antitumor activity and limit drug toxicity.

EXPERIMENTAL DESIGN

In vitro, human GBM cell lines and GSCs were treated with etoposide alone, oncolytic herpes simplex virus (oHSV) G47Δ alone, or the combination. Cytotoxic interactions were analyzed using the Chou-Talalay method, and changes in caspase-dependent apoptosis and cell cycle were determined. In vivo, the most etoposide-resistant human GSC, BT74, was implanted intracranially and treated with either treatment alone or the combination. Analysis included effects on survival, therapy-associated adverse events, and histologic detection of apoptosis.

RESULTS

GSCs varied in their sensitivity to etoposide by over 50-fold in vitro, whereas their sensitivity to G47Δ was similar. Combining G47Δ with low-dose etoposide was moderately synergistic in GSCs and GBM cell lines. This combination did not enhance virus replication, but significantly increased apoptosis. In vivo, the combination of a single cycle of low-dose etoposide with G47Δ significantly extended survival of mice-bearing etoposide-insensitive intracranial human GSC-derived tumors.

CONCLUSIONS

The combination of low-dose etoposide with G47Δ increases survival of mice-bearing intracranial human GSC-derived tumors without adverse side effects. These results establish this as a promising combination strategy to treat resistant and recurrent GBM.

The ribonucleotide reductase R1 subunits of herpes simplex virus 1 and 2 protect cells against poly(I · C)-induced apoptosis

We recently provided evidence that the ribonucleotide reductase R1 subunits of herpes simplex virus types 1 and 2 (HSV-1 and -2) protect cells against tumor necrosis factor alpha- and Fas ligand-induced apoptosis by interacting with caspase 8. Double-stranded RNA (dsRNA) is a viral intermediate known to initiate innate antiviral responses. Poly(I · C), a synthetic analogue of viral dsRNA, rapidly triggers caspase 8 activation and apoptosis in HeLa cells. Here, we report that HeLa cells after HSV-1 and HSV-2 infection were quickly protected from apoptosis caused by either extracellular poly(I · C) combined with cycloheximide or transfected poly(I · C). Cells infected with the HSV-1 R1 deletion mutant ICP6Δ were killed by poly(I · C), indicating that HSV-1 R1 plays a key role in antiapoptotic responses to poly(I · C). Individually expressed HSV R1s counteracted caspase 8 activation by poly(I · C). In addition to their binding to caspase 8, HSV R1s also interacted constitutively with receptor-interacting protein 1 (RIP1) when expressed either individually or with other viral proteins during HSV infection. R1(1-834)-green fluorescent protein (GFP), an HSV-2 R1 deletion mutant protein devoid of antiapoptotic activity, did not interact with caspase 8 and RIP1, suggesting that these interactions are required for protection against poly(I · C). HSV-2 R1 inhibited the interaction between the Toll/interleukin-1 receptor domain-containing adaptor-inducing beta interferon (IFN-β) (TRIF) and RIP1, an interaction that is essential for apoptosis triggered by extracellular poly(I · C) plus cycloheximide or TRIF overexpression. TRIF silencing reduced poly(I · C)-triggered caspase 8 activation in mock- and ICP6Δ-infected cells, confirming that TRIF is involved in poly(I · C)-induced apoptosis. Thus, by interacting with caspase 8 and RIP1, HSV R1s impair the apoptotic host defense mechanism prompted by dsRNA.

Novel viral vectors utilizing intron splice-switching to activate genome rescue, expression and replication in targeted cells

BACKGROUND

The outcome of virus infection depends from the precise coordination of viral gene expression and genome replication. The ability to control and regulate these processes is therefore important for analysis of infection process. Viruses are also useful tools in bio- and gene technology; they can efficiently kill cancer cells and trigger immune responses to tumors. However, the methods for constructing tissue- or cell-type specific viruses typically suffer from low target-cell specificity and a high risk of reversion. Therefore novel and universal methods of regulation of viral infection are also important for therapeutic application of virus-based systems.

METHODS

Aberrantly spliced introns were introduced into crucial gene-expression units of adenovirus vector and alphavirus DNA/RNA layered vectors and their effects on the viral gene expression, replication and/or the release of infectious genomes were studied in cell culture. Transfection of the cells with splice-switching oligonucleotides was used to correct the introduced functional defect(s).

RESULTS

It was demonstrated that viral gene expression, replication and/or the release of infectious genomes can be blocked by the introduction of aberrantly spliced introns. The insertion of such an intron into an adenovirus vector reduced the expression of the targeted gene more than fifty-fold. A similar insertion into an alphavirus DNA/RNA layered vector had a less dramatic effect; here, only the release of the infectious transcript was suppressed but not the subsequent replication and spread of the virus. However the insertion of two aberrantly spliced introns resulted in an over one hundred-fold reduction in the infectivity of the DNA/RNA layered vector. Furthermore, in both systems the observed effects could be reverted by the delivery of splice-switching oligonucleotide(s), which corrected the splicing defects.

CONCLUSIONS

Splice-switch technology, originally developed for genetic disease therapy, can also be used to control gene expression of viral vectors. This approach represents a novel, universal and powerful method for controlling gene expression, replication, viral spread and, by extension, virus-induced cytotoxic effects and can be used both for basic studies of virus infection and in virus-based gene- and anti-cancer therapy.

A novel oncolytic herpes simplex virus that synergizes with phosphoinositide 3-kinase/Akt pathway inhibitors to target glioblastoma stem cells

PURPOSE

To develop a new oncolytic herpes simplex virus (oHSV) for glioblastoma (GBM) therapy that will be effective in glioblastoma stem cells (GSC), an important and untargeted component of GBM. One approach to enhance oHSV efficacy is by combination with other therapeutic modalities.

EXPERIMENTAL DESIGN

MG18L, containing a U(S)3 deletion and an inactivating LacZ insertion in U(L)39, was constructed for the treatment of brain tumors. Safety was evaluated after intracerebral injection in HSV-susceptible mice. The efficacy of MG18L in human GSCs and glioma cell lines in vitro was compared with other oHSVs, alone or in combination with phosphoinositide-3-kinase (PI3K)/Akt inhibitors (LY294002, triciribine, GDC-0941, and BEZ235). Cytotoxic interactions between MG18L and PI3K/Akt inhibitors were determined using Chou-Talalay analysis. In vivo efficacy studies were conducted using a clinically relevant mouse model of GSC-derived GBM.

RESULTS

MG18L was severely neuroattenuated in mice, replicated well in GSCs, and had anti-GBM activity in vivo. PI3K/Akt inhibitors displayed significant but variable antiproliferative activities in GSCs, whereas their combination with MG18L synergized in killing GSCs and glioma cell lines, but not human astrocytes, through enhanced induction of apoptosis. Importantly, synergy was independent of inhibitor sensitivity. In vivo, the combination of MG18L and LY294002 significantly prolonged survival of mice, as compared with either agent alone, achieving 50% long-term survival in GBM-bearing mice.

CONCLUSIONS

This study establishes a novel therapeutic strategy: oHSV manipulation of critical oncogenic pathways to sensitize cancer cells to molecularly targeted drugs. MG18L is a promising agent for the treatment of GBM, being especially effective when combined with PI3K/Akt pathway-targeted agents.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Oncolytic virotherapy reaches adolescence

Lytic viruses kill cells as a consequence of their normal replication life cycle. The idea of harnessing viruses to kill cancer cells arose over a century ago, before viruses were even discovered, from medical case reports of infections associated with cancer remissions. Since then, there has been no shortage of hype, hope, or fear regarding the prospect of oncolytic virotherapy for cancer. Early developments in the field included encouraging antitumor efficacy both in animal studies in the 1920s-1940s and in human clinical trials in the 1950s-1970s. Despite its long-standing history, oncolytic virotherapy was an idea ahead of its time. Without needed advances in molecular biology, virology, immunology, and clinical research ethics, early clinical trials resulted in infectious complications and were fraught with controversial research conduct, so that enthusiasm in the medical community waned. Oncolytic virotherapy is now experiencing a major growth spurt, having sustained numerous laboratory advances and undergone multiple encouraging adult clinical trials, and is now witnessing the emergence of pediatric trials. Here we review the history and salient biology of the field, including preclinical and clinical data, with a special emphasis on those agents now being tested in pediatric cancer patients.